Method for monitoring environmental degradation of adhesive bonds

A contact, dual channel angle beam ultrasonic spectroscopy system was developed for monitoring the environmental degradation of adhesive bonds. Using different surface pretreatments, bonded samples were prepared and exposed to an accelerated environmental degradation process - immersion in a saturated NaCl solution at 341 K (154 °F) and 4.5 kN (1000 lbf) load. Simultaneous normal and angle beam ultrasonic scans were made over the bonded area and reconstruction was performed to estimate the bondline properties' degradation. The reconstructed properties are effective shear and longitudinal moduli, density, thickness and wave attenuations. It is shown that the ultrasonic results provide information on damage evolution prior to failure. Specifically, adhesive creep and bondline property variation are identified as failure precursors measurable by this method.